1. Field of the Invention
The subject invention generally pertains to refrigerant systems and more specifically to a compressor discharge valve that provides freeze and charge migration protection.
2. Description of Related Art
Various valves have been developed to ensure a refrigerant compressor has adequate lubrication at startup. Such valves typically restrict a compressor's initial discharge of refrigerant to quickly increase the discharge pressure so that the pressure is sufficient to force lubricant back to the compressor. Examples of such valves are disclosed in U.S. Pat. No. 5,134,856 (Pillis) and U.S. Pat. No. 5,170,640 (Heitmann).
The Pillis valve includes a piston with a bleed hole (50) that allows high-pressure refrigerant to flow from a front side of the piston to a back side of the piston. Opening a solenoid valve (46) releases the high-pressure refrigerant at the back side of the piston so that the high-pressure refrigerant at the piston's front side can force the valve open. The addition of solenoid valve (46) and having to control it is a drawback of the Pillis valve.
The Heitmann valve opens by using refrigerant at discharge pressure to force a piston (34) away from its valve seat (30). To avoid chatter when the valve is fully open, piston (34) bottoms out against a plate (40). Chatter might still occur, however, when the valve first begins opening. Just before the valve opens, for instance, a buildup of discharge pressure might be barely enough to start opening the valve. Once slightly open, the valve might pass enough refrigerant to decrease the discharge pressure to a point where the valve closes. With the valve closed, discharge pressure can once again build to open the valve back up. A repeat of such a cycle in rapid succession can result in chatter. Other causes of rapidly fluctuating discharge pressure can also be a source of valve chatter.
Consequently, there appears to be an ongoing need for a simple and effective discharge valve for a refrigerant compressor.